Re: [PATCH net-next 3/4] selftests/net: Add netkit io_uring ZC test for large rx_buf_len

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Wed, Jun 10, 2026 at 10:03:43AM +0200, Daniel Borkmann wrote:
> Add test_iou_zcrx_large_buf, which runs iou-zcrx with rx_buf_len >
> page size (-x 2) through a netkit-leased RX queue. The netkit ifindex
> is opaque to io_uring, but rx_page_size is honoured by the leased
> physical qops via netif_mp_open_rxq()'s lease redirect.
> 
> Originally, I also added a BIG TCP variant on top, but dropped it
> here as fbnic (and the QEMU fbnic model) has no BIG TCP support
> to exercise it as this point.
> 
> Tested against the QEMU fbnic emulation. The new test exercises
> the > page rx_buf_len path only when the leased NIC advertises
> QCFG_RX_PAGE_SIZE; otherwise it skips.
> 
> For fbnic, I used Bjorn's patches locally [0]:
> 
>   # ./nk_qlease.py
>   TAP version 13
>   1..5
>   ok 1 nk_qlease.test_iou_zcrx
>   ok 2 nk_qlease.test_iou_zcrx_large_buf
>   ok 3 nk_qlease.test_attrs
>   ok 4 nk_qlease.test_attach_xdp_with_mp
>   ok 5 nk_qlease.test_destroy
>   # Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Without those patches (aka not advertising QCFG_RX_PAGE_SIZE):
> 
>   # ./nk_qlease.py
>   TAP version 13
>   1..5
>   ok 1 nk_qlease.test_iou_zcrx
>   ok 2 nk_qlease.test_iou_zcrx_large_buf # SKIP Large chunks are not supported -95
>   ok 3 nk_qlease.test_attrs
>   ok 4 nk_qlease.test_attach_xdp_with_mp
>   ok 5 nk_qlease.test_destroy
>   # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:1 error:0
> 
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Link: https://lore.kernel.org/netdev/20260522113225.241337-1-bjorn@kernel.org/ [0]
> ---
>  .../selftests/drivers/net/hw/nk_qlease.py     | 86 ++++++++++++++++++-
>  1 file changed, 85 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/drivers/net/hw/nk_qlease.py b/tools/testing/selftests/drivers/net/hw/nk_qlease.py
> index fee114676fd8..90d688453ddf 100755
> --- a/tools/testing/selftests/drivers/net/hw/nk_qlease.py
> +++ b/tools/testing/selftests/drivers/net/hw/nk_qlease.py
> @@ -32,6 +32,15 @@ from lib.py import (
>  )
>  from lib.py import KsftSkipEx, CmdExitFailure
>  
> +# iou-zcrx exits with 42 from setup_zcrx() when the NIC does not advertise
> +# QCFG_RX_PAGE_SIZE (or otherwise rejects the requested rx_buf_len).
> +SKIP_CODE = 42
> +
> +
> +def _restore_hugepages(count):
> +    with open("/proc/sys/vm/nr_hugepages", "w", encoding="utf-8") as f:
> +        f.write(str(count))
> +
>  
>  def _create_netkit_pair(cfg, rxqueues=2):
>      if cfg.nk_host_ifname:
> @@ -188,6 +197,75 @@ def test_iou_zcrx(cfg) -> None:
>          cmd(tx_cmd, host=cfg.remote)
>  
>  
> +def test_iou_zcrx_large_buf(cfg) -> None:
> +    """iou-zcrx with rx_buf_len > page size, going through a netkit-leased
> +    queue. Exercises the queue rx-buf-len path via netif_mp_open_rxq()'s
> +    lease redirect: the netkit ifindex is opaque to io_uring, but
> +    rx_page_size is honoured by the *physical* qops because the lease
> +    pointer rewrites the request from netkit onto the leased physical
> +    rxq before supported_params/validate_qcfg are consulted.
> +    """
> +    cfg.require_ipver("6")
> +    src_queue, nk_queue = _setup_lease(cfg)
> +    defer(_teardown_netkit, cfg)
> +    ethnl = EthtoolFamily()
> +
> +    with open("/proc/sys/vm/nr_hugepages", "r+", encoding="utf-8") as f:
> +        nr_hugepages = int(f.read().strip())
> +        if nr_hugepages < 64:
> +            f.seek(0)
> +            f.write("64")
> +            defer(_restore_hugepages, nr_hugepages)
> +
> +    rings = ethnl.rings_get({"header": {"dev-index": cfg.ifindex}})
> +    rx_rings = rings["rx"]
> +    hds_thresh = rings.get("hds-thresh", 0)
> +
> +    ethnl.rings_set(
> +        {
> +            "header": {"dev-index": cfg.ifindex},
> +            "tcp-data-split": "enabled",
> +            "hds-thresh": 0,
> +            "rx": 64,
> +        }
> +    )
> +    defer(
> +        ethnl.rings_set,
> +        {
> +            "header": {"dev-index": cfg.ifindex},
> +            "tcp-data-split": "unknown",
> +            "hds-thresh": hds_thresh,
> +            "rx": rx_rings,
> +        },
> +    )
> +
> +    ethtool(f"-X {cfg.ifname} equal {src_queue}")
> +    defer(ethtool, f"-X {cfg.ifname} default")
> +
> +    flow_rule_id = set_flow_rule(cfg, src_queue)
> +    defer(ethtool, f"-N {cfg.ifname} delete {flow_rule_id}")
> +
> +    # -x 2 asks iou-zcrx for rx_buf_len = 2 * page_size (8 KiB on x86_64),
> +    # backed by a 2 MiB hugepage area so the chunks are physically
> +    # contiguous, which is what zcrx requires for non-default rx_buf_len.
> +    rx_cmd = (
> +        f"ip netns exec {cfg.netns.name} {cfg.bin_local} "
> +        f"-s -p {cfg.port} -i {cfg.nk_guest_ifname} -q {nk_queue} -x 2"
> +    )

Could cmd(..., ns=cfg.netns) be used instead of ip netns exec?

> +    tx_cmd = f"{cfg.bin_remote} -c -h {cfg.nk_guest_ipv6} -p {cfg.port} -l 12840"
> +
> +    # Probe via -d (dry run): exits with SKIP_CODE if the leased physical
> +    # qops doesn't advertise QCFG_RX_PAGE_SIZE (e.g. older bnxt FW/HW).
> +    probe = cmd(rx_cmd + " -d", fail=False)
> +    if probe.ret == SKIP_CODE:
> +        msg = probe.stdout.strip() or "rx_buf_len not supported by leased NIC"
> +        raise KsftSkipEx(msg)

Since -d can still install an mp, does this also need mp_clear_wait()?

The rest below looks good to me!

Best,
Bobby

> +
> +    with bkg(rx_cmd, exit_wait=True):
> +        wait_port_listen(cfg.port, proto="tcp", ns=cfg.netns)
> +        cmd(tx_cmd, host=cfg.remote)
> +
> +
>  def test_attrs(cfg) -> None:
>      cfg.require_ipver("6")
>      src_queue, nk_queue = _setup_lease(cfg)
> @@ -350,7 +428,13 @@ def main() -> None:
>          cfg.port = rand_port()
>  
>          ksft_run(
> -            [test_iou_zcrx, test_attrs, test_attach_xdp_with_mp, test_destroy],
> +            [
> +                test_iou_zcrx,
> +                test_iou_zcrx_large_buf,
> +                test_attrs,
> +                test_attach_xdp_with_mp,
> +                test_destroy,
> +            ],
>              args=(cfg,),
>          )
>      ksft_exit()
> -- 
> 2.43.0
>